Predisposing factors can be identified in up to 80% of patients who develop cerebral venous thombosis (CVT).1 In many patients risk factors are acquired but 10 to 15% of patients may have inherited tendencies to thrombosis. Deficiencies of protein C, protein S, or antithrombin are reported in large series. The recently identified factor V Leiden mutation (FVR506Q) giving rise to activated protein C resistance is one of the most prevalent genetic mutations currently identified (10% to 15% of the white population),2 and it is now known to be an important risk factor for cerebral venous thrombosis.3-6 All of these thrombophilic tendencies, and particularly the factor V Leiden mutation, are compounded by other factors such as the oral contraceptive pill, pregnancy, pueperium, or immobility.

Prothrombin is a precursor of the serine protease thrombin and is a key enzyme in the process of haemostasis. Recently, a single nucleotide substitution (G to A) at position 20210 in the 3’ untranslated region of the gene encoding prothrombin has been identified.7 Its heterozygous state, 20210A, is a risk factor for the development of deep vein thromboses,7 8 and it has recently been implicated in …